import java.util.Scanner;

public class 输入r求出圆的面积 {
    final static double PI = 3.14159265358979323;
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        int n = scanner.nextInt();
        double mianji = PI*n*n;
        System.out.printf("%.7f",mianji);
    }
}
